Analysis of the Fe X and Fe XIV line width in the solar corona using LASCO-C1 spectral data

Abstract

Aims:The purpose of this paper is to analyze the variation in the line width with height in the inner corona (region above 1.1 R_⊙), by using the spectral data from LASCO-C1 aboard SOHO. We used data acquired at activity minimum (August-October 1996) and during the ascending phase of the solar cycle (March 1998).
Methods: Series of images acquired at different wavelengths across the Fe X 637.6 nm (red) and Fe XIV 530.3 nm (green) coronal lines by LASCO-C1 allowed us to build radiance and width maps of the off-limb solar corona.
Results: In 1996, the line width of Fe XIV was roughly constant or increased with height up to around 1.3 R_⊙ and then it decreased. The Fe X line width increased with height up to the point where the spectra were too noisy to allow line width measurements (around 1.3 R_⊙). Fe X showed higher effective temperatures as compared with Fe XIV. In 1998 the line width of Fe XIV was roughly constant with height above the limb (no Fe X data available).